To further increase efficiency of a system spectrum and effectively resist the selective frequency fading of a radio channel, orthogonal frequency division multiple access (OFDMA) is adopted in the long term evolution (LTE) project of the 3rd generation (3G) mobile communications system. With OFDMA, the information about all terminals within a cell is carried on different carriers that are mutually orthogonal. All interference in the cell comes from other adjacent cells. A terminal in the central area of the cell (hereinafter referred to as “central terminal”) is near to the base station of the cell and the interference signals of adjacent cells are far from the base station of the cell. The signal interference ratio (SIR) is therefore relatively high for the central terminal. For a terminal located in the edge area of the cell (hereinafter referred to as “edge terminal”), because users using the same carrier resource in the adjacent cells impose strong interference on the terminal and the terminal is far from the base station of the cell, the SIR is relatively low. As a result, the quality of service (QoS) of users at the cell edge is poor and the throughput is small. In LTE, therefore, ICI suppression techniques are very important.
In a method for suppressing ICI provided in the prior art, the base station divides channel resources of the cell into central channel group and edge channel group. The central channels of adjacent cells support soft frequency reuse and the edge channels of adjacent cells are orthogonal. Because central users of adjacent cells are far apart, the interference between them is weak. Therefore, the same frequency may be reused by the central channels of adjacent cells, which is known as soft frequency reuse. Because the edge channels of adjacent cells are orthogonal, the interference between edge terminals in the adjacent cells is effectively avoided. The base station may divide the central channel group and the edge channel group according to the transmit power, or distance, or channel SIR. The base station may detect the pilot information reported by a terminal to determine whether the terminal is an edge terminal or a central terminal. If the terminal is an edge terminal, the base station selects a channel of the highest SIR from an edge channel group and assigns the channel to the edge terminal. If the terminal is a central terminal, the base station selects a channel of the highest SIR from a central channel group and assigns the channel to the central terminal.
The inventor finds that when the above method is used to divide central channel group and edge channel group, where central channels of adjacent cells support soft frequency reuse and edge channels are orthogonal, ICI can be suppressed to a certain extent. When there are few or no edge terminals, however, edge channels to be assigned to edge terminals will not be assigned to central terminals; or when there are few or no central terminals, central channels to be assigned to the central terminals will not be assigned to edge terminals. This causes a waste of channel resources.